Milk pasteurization || Type of Milk pasteurization

MILK PASTEURIZATION

• The term as applied to milk refers to heating every particle of milk to a temperature of at least 63°C (145.4 F) for 30 min or 71.7°C (161F) for 15 sec (or an equivalent time-temperature combination). The processed milk is to be immediately cooled to 4°C and stored at a temperature of 4°C( International Dairy Federation (IDF) has defined Pasteurization as a process applied to a product with an objective of minimizing possible health hazard arising from pathogenic microorganisms associated with milk by heat treatment, which is consistent with minimal chemical, physical and organoleptic changes in the product. The heat treatment suggested by the IDF for pasteurization of milk are 15 sec at 71.7°C=161F or 30 min at 62.8°C=145oF which can be regarded as internationally accepted norm. Primarily pasteurization addresses two concerns viz., safety (public health aspects) and keeping quality.

Types of pasteurization plants 

1. Batch/Holding/Low temperature long time (LTLT)

• This method uses a double jacketed vat with in-built provision of circulating water, steam or heating coils of water or steam. The vat is equipped with an agitator to ensure slow agitation while milk is either heated or cooled. The milk is brought to the desired temperature, held for a definite period and then cooled. The milk can be alternatively taken out hot and cooling done in surface cooler/plate chiller to increase the plant capacity. Agitation ensures rapid heat transfer during heating or cooling and agitators with different design features are available which includes double walled paddles or design with internal steam or water circulation. The inlet valve positioned at the bottom is preferred as it reduces foam formation thereby improving efficiency of the plant.  The essential components of a batch pasteurizer are: insulated outer stainless steel body, insulated hinged stainless steel lid, inner body made of steel, agitator and motor, outlet valve and connections for hot and cold water. 

2.High temperature short time (HTST)

• It is a continuous process and offers advantages over batch method in terms of saving in time and energy. This system uses plate heat exchanger (PHE) which comprises of several corrugated stainless steel plates stacked together and held in place on a frame.
• The milk enters from the raw milk tank, gets pre-heated in the regeneration section through the outgoing milk (72°C) and passes subsequently through a clarifier before homogenization. The homogenized milk is heated in the heating section and held in the holding tube at 72°C for 15 sec. The flow diversion valve (FDV) diverts the milk to feed tank if it is not properly pasteurized or directs properly pasteurized milk to the regeneration section where its temperature gets substantially reduced before entering the cooling section for final cooling to 4°C.
• Plate heat exchanger is the heart of HTST pasteurizer. The plates are made of stainless steel sheets, usually rectangular in shape. The corrugations on the plates are so designed that they cause turbulence and increase heat transfer. The efficiency of heat transfer also depends on the total surface area of the plates, the plate thickness, metal of construction and the difference in temperature of the milk and the heating/cooling medium.

Saiyad Azharuddin
B.tech ( Dairy Technologist)